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  • 1
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    Investigation B: Laminar confined coaxial entrance flow with heat generation (1975)
    In:  CASI
    Details
    Publication Date: 2009-11-16
    Description: The results of a parametric study on the entrance flow region in a gas core nuclear reactor are presented. The physical system is modeled as laminar confined, coaxial flow with heat generation in the inner fluid. The governing equations include the boundary layer approximations and the assumptions of only radial radiative transport of energy represented as an energy diffusion term. The Von Mises transformation and a zeta transformation are used to transform the equations into nonlinear nonhomogeneous convective-diffusion equations. A unique combination of forward and backward difference equations which yields accurate results at moderate computational times, is used in the numerical method. Results show that the rapidly accelerating, heat generating inner stream actually shrinks in radius as it expands axially.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Turbulence Coefficients and Stability Studies for the Coaxial Flow or Dissimiliar Fluids; 76 p
    Format: text
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  • 2
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    The free shear layer tone phenomenon and probe interference (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The reported investigation shows that the hot-wire probe induces stable upstream oscillations in a free shear layer, similar to the jet edge tone mechanism. This effect can be significant also in measurements involving large-scale organized structure, conditional sampling, space-time correlation, and convection velocity, when a reference or indicator probe may be used near the origin of the free shear layer. It appears that even in a free shear layer without any wedge, an object in the flow sufficiently downstream can also provide feedback to the flow upstream. A description is given of the edge-tone phenomenon which is observed when a thin slit jet impinges on a plane wedge. Attention is given to the free shear layer tone induced by a hot-wire probe, the free shear layer tone phenomenon, and shear layer tone eigenvalues and eigenfunctions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics; 87; July 26
    Format: text
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  • 3
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    The free shear layer edgetone and instability measurements (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The hot-wire probe is known to be capable of triggering and sustaining upstream instability modes like the slit jet-wedge edgetone termed the free shear layer tone. In this paper, the hot-wire probe is used to investigate the shear tone phenomenon in axisymmetric and plane free shear layers. For all the measurements reported, the initial boundary layers producing the free shear layers are documented (at 0.2 cm upstream from the lip) and classified as laminar. It is shown that the free shear layer, inherently different from the fully vortical slit jet, produces a different tone behavior. The data on the free shear layer tone eigenfunctions and eigenvalues suggest that the feedback is hydrodynamic rather than acoustic.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: Structure and mechanisms of turbulence II; Proceedings of the Symposium on Turbulence; Aug 01, 1977 - Aug 05, 1977; Berlin
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  • 4
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    Acoustics-turbulence interaction (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An investigation of the instability frequency was undertaken. Measurements revealed that the hot wire probe induces and sustains stable upstream oscillation of the free shear layer. The characteristics of the free shear layer tone are found to be different from the slit jet wedge edgetone phenomenon. The shear tone induced by a plane wedge in a plane free shear layer was then examined in order to further document the phenomenon. The eigenvalues and eigenfunctions of the tone fundamental show agreement with the spatial stability theory. A comprehensive summary of the results is also included.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-155178
    Format: application/pdf
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  • 5
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    An experimental study of a self-confined flow with ring-vorticity distribution (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A new form of self-confined flow was investigated in which a recirculation zone forms away from any solid boundary. An inviscid flow analysis indicated that in a purely meridional axisymmetric flow a stationary, spherical, self-confined region should occur in the center of a streamlined divergent-convergent enlargement zone. The spherical confinement region would be at rest and at constant pressure. Experimental investigations were carried out in a specially built test apparatus to establish the desired confined flow. The streamlined divergent-convergent interior shape of the test section was fabricated according to the theoretical calculation for a particular streamline. The required inlet vorticity distribution was generated by producing a velocity profile with a shaped gauze screen in the straight pipe upstream of the test section. Fluid speed and turbulence intensity were measured with a constant-temperature hot-wire anemometer system. The measured results indicated a very orderly and stable flow field.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-135104
    Format: application/pdf
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  • 6
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    Investigations of coherent structures in free turbulent shear flows (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The dynamics of large-scale coherent structures in general, and studies based on flow-visualization and phase-locked hot-wire measurements of the structures in the near fields of circular jets are considered. A study involving the nature of coherent structures under conditions of stable vortex pairing induced by controlled axisymmetric acoustic excitation reveals that azimuthal coherence initially enhanced by the excitation is lost before the end of the potential core through evolution of azimuthal lobe structures and turbulent breakdown. The evolution of a spark-induced spot in an axisymmetric turbulent mixing layer is also investigated, and the coherent Reynolds stress associated with the spot is found to be much higher than the background turbulence Reynolds stress. In addition, the state of organization in a high Reynolds number unperturbed axisymmetric mixing layer is examined, and it is shown that the shear layer is infrequently organized and the motions are intensely three-dimensional, while tearing and fractional pairing occur as frequently as complete pairing.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Biennial Symposium on Turbulence; Oct 08, 1979 - Oct 10, 1979; Rolla, MO
    Format: text
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  • 7
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    Flow tracing fidelity of scattering aerosol in laser Doppler velocimetry (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An experimental method for the determination of the flow-tracing fidelity of a scattering aerosol used in laser Doppler velocimeters was developed with particular reference to the subsonic turbulence measurements. The method employs the measurement of the dynamic response of a flow-seeding aerosol excited by acoustic waves. The amplitude and frequency of excitation were controlled in order to simulate the corresponding values of fluid turbulence components. Experimental results are presented on the dynamic response of aerosols over the size range from 0.1 to 2.0 microns in diam and over the frequency range 100 Hz to 100 kHz. It was observed that unit-density spherical scatterers with diameters of 0.2 micron followed subsonic air turbulence frequency components up to 100 kHz with 98% fidelity.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Applied Optics; 14; Apr. 197
    Format: text
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